Institut Straumann AG (Basel, Switzerland) markets a hand tool for dentistry and/or dental prosthetics which is made up of a cylindrical grip part, a collet element and an actuating device, the grip part having, in the front end area, an external thread and also a receiving recess in the form of a blind bore along the main axis of the cylindrical grip part. The collet element is partially engaged in this receiving recess and is used to receive a rotationally symmetrical object that is to be worked (e.g., rotated during use). At its front end area projecting beyond the grip part, the collet element has an external cone envelope surface tapering toward the free end. The actuating device in the form of a cap-like union nut, which can be screwed on over the external thread in the front end area of the grip part, has, inside a passage, a bearing surface acting as a mating piece for the cone envelope surface of the collet element. Through this passage, the object to be clamped is introduced from the outside into the collet element completely surrounded by the union nut and the receiving recess. Because of the pressure exerted on its cone envelope surface via the bearing surface of the union nut, the collet element is pressed toward the base of the receiving recess in the grip part. A rotational movement of the union nut about the main axis, relative to the grip part, changes the pressure exerted via the support surface on the cone envelope surface of the collet element, with the result that a cylindrical recess in the clamping area of the collet element changes in diameter and the object to be worked can be clamped or released, respectively.
Since the existing hand tool is designed for working a rotationally symmetrical object, handling problems may arise if it is used on an object which is not rotationally symmetrical. The position of the object may inadvertently change during the clamping procedure.
It would thus be desirable to provide a hand tool which is easy to handle and is able to hold an object which is not rotationally symmetrical, for example a secondary element for a dental prosthesis, a dental crown or a model.